Engines may use various forms of fuel delivery to provide a desired amount of fuel for combustion in each cylinder. One type of fuel injection, or delivery, uses a port injector for each cylinder to deliver fuel to respective cylinders. Another type of fuel injection uses a direct injector for each cylinder. Engines have also been described using more than one injector to provide fuel to a single cylinder in an attempt to improve engine performance.
One such example (US 2007/0119422 A1) describes a flexible multiple-fuel engine using both port and direct injection, where different fuel types are provided to the injectors. For example, direct injection of ethanol may be used with port injected gasoline to address knock limitations, especially under boosted conditions. In this example, a desired setting for the various fuels may be predetermined using engine maps, and then adjusted based on feedback from a knock sensor, along with a spark retard, to mitigate the knock. Specifically, the effective knock suppression of the fuels can be varied responsive to operating conditions to improve engine efficiency while meeting engine output requirements.
However, the inventor herein has recognized several issues with such an approach. As one example, one particular cylinder may be more prone to knocking and consequently may start to develop knock before other cylinders within the engine, especially under certain operating conditions. If direction injection of ethanol is used in all of the cylinders to address knock when less than all of the cylinders may be prone to knock, ethanol may be over-used, and thereby overly depleted.
Thus, in one example, the above issues may be addressed by a method for controlling engine operation of an engine having a plurality of cylinders, each cylinder including a first and second injector for delivering fuel to the cylinder, the method comprising: operating a first cylinder to combust fuel delivered from both the first and second fuel injector of the first cylinder, and operating a second cylinder to combust fuel delivered from only one of the first and second fuel injectors of the second cylinder.
In one example, each of the plurality of cylinders of the engine may be capable of operating with a port injection of gasoline and a direct injection of ethanol. As such, a first cylinder may be more prone to knock as compared to the remaining cylinders. Accordingly, a direct injection of ethanol may be enabled at a lower torque, in the first cylinder. Consequently, under similar operating conditions, the first may be operating with direct injected ethanol in addition to port injected gasoline, while the remaining cylinders may be operating with port injected gasoline only. In another example, a first and second cylinder may be more prone to knock as compared to the remaining cylinders. Accordingly, the first and second cylinders may be adjusted together as a cylinder group and a direct injection of ethanol may be enabled in the knock-prone cylinder group at a lower torque, compared to other cylinders or cylinder groups. In this way, by specifically enabling direct injection of ethanol in knock-prone cylinders, or cylinder groups, engine knock may be abated without overly depleting ethanol.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.